Newsprint and similar materials are transported in large, massive rolls in which the sheet material is wound around a central cylindrical core of fiber or cardboard. Such objects are sufficiently heavy that they must be handled by crane for loading and unloading from vessels. They are readily damaged and so must be handled carefully in such loading and unloading. To facilitate loading and unloading such rolls, various core lifting chucks have been developed which have a probe which is inserted into the central cylindrical core of the roll and which grips the central core, to allow the roll to be lifted by a cable from a crane or the like.
For example, U.S. Pat. No. 3,905,636 issued Sep. 16, 1975 to AB Hagglund & Sons discloses a probe device having a lower probe section which is inserted into the hollow core of the paper roll. It consists of an inner component which is attached to the lifting cable and an outer component which is attached to a horizontal plate. Two lifting cables are attached to two long arms which in turn are connected to the inner component so that when the cables lift the ends of the two arms, the inner component is raised and the outer component is pressed downwardly. This causes a cone-shaped lower end of the inner component to force outwardly the ends of a number of pivoting fingers on the lower end of the outer component, which then engage and grip the inner core of the roll. When the roll is returned to the ground and the cables are released, the inner component drops back down, the fingers retract and the probe is removed from the core.
The problem with this existing prior art design is that since it requires two cables and two widely separated lifting arms, it is very cumbersome, heavy and unwieldy to operate, taking two persons to handle it. The width of the two arms, which frequently swing around during the loading process, causes safety problems. The two lines may become tangled. Further, when the fingers engage the cardboard core under considerable force they can become lodged therein and the roll cannot then be released from the probe. To remove the probe from the roll in that case it is necessary to destroy the paper roll at considerable expense and inconvenience. The arms and jaws on this device require frequent greasing to avoid jamming. It is also difficult to adjust the length of the probe. This cannot be done while the probe is in a roll. Also in this device, an operator must engage a locking device so that the probe can be removed from the roll once it is set down on the ground.
There is therefore a need for a compact lifting probe which can be readily removed from the roll core in case of jamming, is readily adjustable, and which is self-releasing when the load is to be released.